To have "thermal comfort" means that a person wearing a normal amount of clothing feels neither too cold nor too warm. Thermal comfort is important both for one's well-being and for productivity. It can be achieved only when the air temperature, humidity and air movement are within the specified range often referred to as the "comfort zone".

Where air movement is virtually absent and when relative humidity can be kept at about 50%, the ambient temperature becomes the most critical factor for maintaining thermal comfort indoors. However, temperature preferences vary greatly among individuals and there is no one temperature that can satisfy everyone. Nevertheless, an office which is too warm makes its occupants feel tired; on the other hand, one that is too cold causes the occupants' attention to drift, making them restless and easily distracted. Workers begin worrying about how to get warm again.

Maintaining constant thermal conditions in the offices is important. Even minor deviation from comfort may be stressful and affect performance and safety. Workers already under stress are less tolerant of uncomfortable conditions.

A general recommendation is that the temperature be held constant in the range of 21-23°C (69-73°F). In summertime when outdoor temperatures are higher it is advisable to keep air-conditioned offices slightly warmer to minimize the temperature discrepancy between indoors and outdoors.

When relative humidity is kept at about 50%, office workers have fewer respiratory problems (specifically in the winter) and generally feel better. Higher humidity makes the office feel "stuffy". More important, it can contribute to the development of bacterial and fungal growth (especially in sealed buildings).

Humidity lower then 50% causes discomfort by drying out the mucous membranes, contributing to skin rashes. Dry conditions cause electrostatic charge on both office equipment and their users.

Air velocities below 0.25 metres/second (or about 50 feet/minute) does not create any significant distraction even in tasks requiring sustained attention.

The CSA Standard CAN/CSA Z412-00 - "Office Ergonomics" gives acceptable ranges of temperature and relative humidity for offices in Canada. These values are the same as recommended by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Standard 55 - 2004 "Thermal Environmental Conditions for Human Occupancy". The recommended temperature ranges have been found to meet the needs of at least 80% of individuals. Some people may feel uncomfortable even if these values are met. Additional measures may be required.

Source: Adapted from ASHRAE 55-2004.

Table 2 shows acceptable temperatures ranges for relative humidity levels of 30% and 60%, as recommended by the National Research Council of Canada.

Source: National Research Council (Canada) Indoor Air Quality and Thermal Comfort in Open-Plan Offices, Construction Technology Update No. 64 , October 2005
http://irc.nrc-cnrc.gc.ca/pubs/ctus/64_e.html

Table 3 summarizes some typical responses to various temperatures.

Table 3
Temperature
°F	°C
78	25	Optimal for bathing, showering. Sleep is disturbed
75	24	People feel warm, lethargic and sleepy. Optimal for unclothed people.
72	22	Most comfortable year-round indoor temperature for sedentary people.
70	21	Optimum for performance of mental work.
64	18	Physically inactive people begin to shiver. Active people are comfortable.

Document last updated on October 23, 2007

Copyright ©1997-2010 Canadian Centre for Occupational Health & Safety